#!/usr/bin/perl

$pi = atan2(1,1) * 4;

sub distance {
	my ($lat1, $lon1, $lat2, $lon2, $unit) = @_;
	#printf "$lat1, $lon1, $lat2, $lon2\n";
	my $theta = $lon1 - $lon2;
	my $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) + cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));
  $dist  = acos($dist);
  $dist = rad2deg($dist);
  $dist = $dist * 60 * 1.1515;
  if ($unit eq "K") {
  	$dist = $dist * 1.609344;
  } elsif ($unit eq "N") {
  	$dist = $dist * 0.8684;
		}
	return ($dist);
}

#::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
#:::  This function get the arccos function using arctan function   :::
#::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
sub acos {
	my ($rad) = @_;
	my $ret = atan2(sqrt(1 - $rad**2), $rad);
	return $ret;
}

#::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
#:::  This function converts decimal degrees to radians             :::
#::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
sub deg2rad {
	my ($deg) = @_;
	return ($deg * $pi / 180);
}

#::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
#:::  This function converts radians to decimal degrees             :::
#::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
sub rad2deg {
	my ($rad) = @_;
	return ($rad * 180 / $pi);
}

#print distance(32.9697, -96.80322, 29.46786, -98.53506, "M") . " Miles\n";
#print distance(32.9697, -96.80322, 29.46786, -98.53506, "K") . " Kilometers\n";
#print distance(32.9697, -96.80322, 29.46786, -98.53506, "N") . " Nautical Miles\n";